Variation in the restriction map in the Adh region (alcohol dehyrogenase locus) of chromosome Ii of Drosophila melanogaster from natural populations was examined. Insertion/deletion differences were common. All insertions of over 200 nucleotides share sequence homology with known transposable elements. The distribution within Drosophila malanogaster and among related species suggest that such variants are deleterious mutants. Preliminary comparisons of gene activity among inserted and noninserted sequences supports this view.